It is desirable for a power control semiconductor device such as a power MOS transistor or the like to have a high breakdown voltage and a low ON-resistance. For example, in a vertical MOS transistor having a trench gate structure, it is desirable to maintain the breakdown voltage by relaxing the electric field concentration at the periphery of the trench gate. Also, it is desirable to reduce the ON-resistance by widening the current path between adjacent trench gates.